1. Field of the Invention
The present invention relates to a plate check valve for use in a reciprocating compressor or the like, and more particularly to such a valve having seats which are durable and are quickly and economically replaced.
2. Description of the Prior Art
Check valves using movable plates are well known and, typically, are employed in large reciprocating compressors of the type utilized for ammonia refrigeration. However, existing valves of this type have a number of deficiencies. A plate of such a check valve moves toward and from a seat circumscribing a flow passage. When the plate is seated it closes the passage, preventing reverse flow through a cylinder of the compressor. In normal operation of the compressor, the plate impacts the seat at each piston stroke within the cylinder. This normally occurs approximately 340 times a minute. This hammering action of the plate against the seat eventually destroys the seat. In existing valves of this type, the seat is an integral part of a housing for the plate. As a result, the entire housing must be replaced at relatively great expense when the seat is destroyed during the normal operation of the valve.
The seats of plate valves used in closed systems, such as refrigeration systems, are particularly subject to destruction due to movement of a valve plate toward its seat. The piping of such systems is assembled primarily by welding with the result that "trash", relatively hard and irregularly shaped bits of slag and metal from the welding operation, remain in the system. This trash is carried through the system into the compressor check valves where the trash is hammered onto the valve seats by the plates, destroying the seats after the system has operated for a relatively short period of time.
The seats of compressor check valves utilized in refrigeration service are also subject to breakage due to the ingestion of a slug of refrigerant liquid. The stress due to the sudden drop from a vapor temperature of 5.degree. to 10.degree. C. (41.degree. to 50.degree. F.) to a liquid temperature of -29.degree. C. (-20.degree. F.) is frequently sufficient to fracture the valve seats which, typically, are constructed of cast iron or other ferrous materials which are relatively brittle at such temperature. While other materials, such as aluminum alloys, do not become embrittled under refrigerant temperatures, they are too soft to withstand the normal hammering action of the plates when used for a plate valve seat.
Typically, plate check valves for large reciprocating compressors are supplied in replaceable units, each unit having one or more plates and a housing therefor. The housing has a relatively complicated shape since it conforms to the surfaces of the compressor on which the valve is mounted and, typically, is provided with a plurality of plate seats, a plurality of fluid passages, bores for mounting bolts, and the like. As a result, although each valve unit is relatively simple to replace, its cost of replacement is substantial due to the complicated construction of the housing.